As discussed at some length in U.S. Pat. No. 4,874,045, the art of drilling bore holes in the earth has evolved substantially. Initially, a bit was simply threaded onto the end of drill pipe and the resultant bore hole meandered significantly into the earth, typically in a corkscrew manner. At the present time, an attempt to drill a relatively straight vertical bore hole in the earth incorporates an elaborate bottom hole assembly including a series of stabilizers above the bit and a long length of drill collars above and interspersed between stabilizers.
It has become more desirable to drill straight vertical bore holes in the earth as wells are being drilled deeper. This is because of increased friction generated between rotating drill pipe and the bore hole. One can easily visualize that rotating drill pipe from the surface in a 20000′ well consumes considerably more horsepower than in a 5000′ well. Even where wells are drilled with a mud motor, drill pipe is also preferably rotated from the surface in order to increase the rate of penetration. Unduly meandering bore holes, and the friction generated thereby, are accordingly a much greater problem as well depths increase.
Disclosures of interest relative to this invention are found in U.S. Pat. Nos. 3,250,578; 3,938,853; 4,874,045; 5,474,143 and 5,697,460.